It is well known that electronic circuitry must be protected from transient voltage and current conditions which exceed the capacity of the circuitry. Such electrical transients can damage circuit elements and can cause errors in operation. Switching devices such as gas tubes, vacuum gaps, semiconductors such as Zener or avalanche diodes, amorphous semiconductor diodes such as chalcogenides and the like are well known and have been suggested for use as circuit protection devices. However, many of these switching devices are not satisfactory when used in modern electronic equipment, in some cases because of slow response time, short operating cycle life, too high threshold voltage to trigger operation or inability to handle the energies contained in transient pulses resulting from, for example, lightning discharges.
U.S. Pat. No. 3,685,026 discloses a switching element which has finely divided conductive particles having an average particle size from 0.1 to 10 microns dispersed in resin. U.S. Pat. No. 4,726,991 discloses a matrix formed of a mixture of separate particles of conductive materials and separate particles of semiconductor materials coated with insulating material to provide chains of the particles within the matrix with interparticle separation distances along the chain less than several hundred angstroms, thereby to permit quantum-mechanucal tunneling of electrons between the separate particles in response to high energy electrical transients.